Exercise

Discrepancy between actual and predicted means: get intuitive!

As seen in the previous exercise, the actual means do not largely differ among the different departments. There has to be an explanation why the predicted salaries of the professors of the sociology department tend to be lower on average than those of professors of the history department. Remember that the regression coefficient for the sociology department was significantly different from zero in a multiple regression in which a dummy variable for department was included.

How would you explain the apparent discrepancy between the actual and the predicted mean salary of professors across departments? Take a look at the actual means of the other predictor variables years and publications by means of the tapply() function to help you to come up with a well-considered answer.

Instructions

50 XP

Possible Answers

Because sociology professors have less years on the job and less publications on average compared to other departments, their actual mean salary is lower than that of other departments. This causes the discrepancy between actual and predicted mean salaries of the sociology professors.

press 1

Because sociology professors have more years on the job and more publications on average compared to other departments, their actual mean salary is comparable to that of other departments. The discrepancy between actual and predicted salary is solely the consequence of the fact that predicted mean salaries only hold for professors who have an average amount of publications and an average numbers of years of experience across all professors of the university.

press 2

Because sociology professors have less years on the job and less publications on average compared to other departments, their actual mean salary is lower than that of other departments. The discrepancy between actual and predicted salary is solely the consequence of the fact that predicted mean salaries only hold for professors who have an average amount of publications and an average numbers of years of experience across all professors of the university.